Colorectal cancer is the second leading cause of cancer death in the United States, with 135,000 new cases diagnosed each year and an overall 5-year survival rate of ˜50%. Most colorectal cancers develop slowly, beginning as small benign colorectal adenomas that progress over several decades to larger and more dysplastic lesions, eventually becoming malignant. This gradual progression provides ample opportunity for prevention and intervention. Diagnostic screening methods are at present suboptimal; therefore, new approaches are needed.
Early examination for colon cancer is generally performed with the digital rectal examination, sigmoidoscopy, colonoscopy or barium enema.
Digital rectal examination is made to check the normality of colon by an examiner wearing a glove and putting on some lubricant and inserting a hand into the rectum followed by the palpation, sigmoidoscopy is to observe the rectum and colon directly through a long and flexible mirror-attached tube, colonoscopy is to examine inside of the colon directly through an endoscope, and barium enema is to examine the abnormality of the blood stream distributed in the colon after injecting a contrast medium followed by the computed tomography.
The above-mentioned examinations are methods simply to assess the abnormality of the colon and so more precise tissue examination should be followed if lesions of diseases are diagnosed by those methods. For the biopsy performed after identifying lesions of diseases, it is relatively more accurate, but the diagnosis, which accompanies with some pain to patients, is so inconvenient that the patients tend to hesitate to take examinations. Therefore, needs for developing an easy and simple method for diagnosing colon cancer has been continued in the art.
On the other hand, a diagnosis method using genes has been developed for the diseases like cancers occurring genetic mutation and a considerable accomplishment has been reported on lung cancer, liver cancer and stomach cancer, but there are currently not many results reported on colon cancer. The diagnosis using genes is generally performed by PCR using DNA extracted from the tissue suspicious of cancer or by gene expression analysis using cDNA microarray for which RNA is extracted from the tissue. The former is effective only for specific cancers such as chronic myelogenous leukemia (CML) or acute lymphocytic leukemia (ALL) mainly caused by chromosome translocation, and the latter has a drawback that the conventional cancer diagnosis methods such as tissue examination, endoscopy or CT (computerized tomography) scans should precede.
In order to overcome the drawback of the cancer diagnosis methods described above, a method with which detects cancer-specific antigen and diagnoses cancer has been developed. For example, carcinoembryogenic antigen (CEA) has been reported to be a cancer-specific antigen, since the level of CEA is increased in the patients of rectum-colon cancer, stomach cancer, breast cancer, lung cancer, ovary cancer, prostate cancer or pancreas cancer (see: Bowser-Finn, R. A., Kahan, L., Larson, F. C., Traver, M. I. (1986) Tumour Biol. 7, 343-52; Carpelan-Holmstrom, M. A., Haglund, C. H., and Roberts, P. J. (1996) Dis Colon Rectum 39, 799-805). However, even if the cancer patients are diagnosed using CEA, further examination should be made to determine the kind of cancer precisely, which plays a barrier to easy and practical application of CEA in the diagnosis of cancers, since the CEA is commonly expressed in several cancers described above.
In this connection, there are strong reasons for exploring and developing an easy and simple method for diagnosing colon cancer with a high reliability and validity.